Molecular Mechanisms Underlying the Regulation of the MFG-E8 Gene Promoter Activity in Physiological and Inflammatory Conditions

MFGE8 regulates the EndoMT of HLMECs through the BMP signaling pathway and fibrosis in acute lung injury

BACKGROUND

To investigate the effects and mechanisms of MFGE8 on LPS-induced endothelial-to-mesenchymal transition (EndoMT) and pulmonary fibrosis in human lung microvascular endothelial cells (HLMECs) and a mouse model of acute lung injury.

METHODS

Serum MFGE8 levels were compared between ARDS patients and controls. In vitro, HLMECs were treated with LPS, siRNA targeting MFGE8, and recombinant human MFGE8 (rhMFGE8).HLMEC morphology, invasion, migration, and EndoMT markers (CD31, ɑ-SMA) were evaluated. BMP/Smad1/5-Smad4 signaling and Snail expression were assessed via immunofluorescence, western blotting, and qRT-PCR. In vivo, rhMFGE8 effects on pulmonary fibrosis and EndoMT were analyzed in a mouse model of acute lung injury.

RESULTS

MFGE8 levels were significantly reduced in ARDS patients, with higher levels correlating to better survival. In vitro, rhMFGE8 improved HLMEC morphology, reduced invasion and migration, and attenuated LPS-induced EndoMT by increasing CD31 and decreasing α-SMA. MFGE8 knockdown increased BMP/Smad1/5-Smad4 signaling and Snail expression, while rhMFGE8 inhibited these effects. In vivo, rhMFGE8 ameliorated pulmonary fibrosis and EndoMT in mice.

CONCLUSIONS

MFGE8 regulates LPS-induced EndoMT in HLMECs via the BMP/Smad1/5-Smad4 pathway and protects against pulmonary fibrosis in acute lung injury, suggesting it as a therapeutic target for ALI and ARDS.

Emerging Roles for MFG-E8 in Synapse Elimination

Synapse elimination is an essential process in the healthy nervous system and is dysregulated in many neuropathologies. Yet, the underlying molecular mechanisms and under what conditions they occur remain unclear. MFG-E8 is a secreted glycoprotein well known to act as an opsonin, tagging stressed and dying cells for engulfment by phagocytes. Opsonization of cells and debris by MFG-E8 for microglial phagocytosis in the CNS is well established, and its role in astrocytic phagocytosis, and trogocytosis-like engulfment of synapses is beginning to be explored. However, MFG-E8's function in other tissues is highly diverse, and evidence suggests that its role in the nervous system and on synapse elimination in particular may be more complex and varied than opsonization. In this review, we outline the documented direct and indirect effects of MFG-E8 on synapse elimination, while also proposing potential roles to be explored further, in particular, cytoskeletal reorganization of neurites and glia leading to synapse elimination by various mechanisms. Finally, we demonstrate the need for several open questions to be answered-chiefly, under what conditions might MFG-E8-mediated synapse elimination occur in favor of other mechanisms, and when might its activity be dysregulated, increasing unwanted synapse elimination and neurotoxicity?

Identification of DNA methylation associated enrichment pathways in adults with non-specific chronic low back pain

Chronic low back pain (cLBP) that cannot be attributable to a specific pathoanatomical change is associated with high personal and societal costs. Still, the underlying mechanism that causes and sustains such a phenotype is largely unknown. Emerging evidence suggests that epigenetic changes play a role in chronic pain conditions. Using reduced representation bisulfite sequencing (RRBS), we evaluated DNA methylation profiles of adults with non-specific cLBP (n = 50) and pain-free controls (n = 48). We identified 28,325 hypermethylated and 36,936 hypomethylated CpG sites (p < 0.05). After correcting for multiple testing, we identified 159 DMRs (q < 0.01and methylation difference > 10%), the majority of which were located in CpG island (50%) and promoter regions (48%) on the associated genes. The genes associated with the differentially methylated regions were highly enriched in biological processes that have previously been implicated in immune signaling, endochondral ossification, and G-protein coupled transmissions. Our findings support inflammatory alterations and the role of bone maturation in cLBP. This study suggests that epigenetic regulation has an important role in the pathophysiology of non-specific cLBP and a basis for future studies in biomarker development and targeted interventions.

Interferon-γ inhibits sirtuin 6 gene expression in intestinal epithelial cells through a microRNA-92b-dependent mechanism

Sirtuin 6 (Sirt6) is predominantly expressed in epithelial cells in intestinal crypts. It plays an important role in protecting intestinal epithelial cells against inflammatory injury. Previously, we found that colitis is associated with the downregulation of Sirt6 protein in the intestines. Here, we report that murine interferon-γ (Ifnγ) inhibits Sirt6 protein but not mRNA expression in young adult mouse colonocytes (YAMC, a mouse colonic epithelial cell line) in a dose- and time-dependent manner. Using microRNA array analysis, we showed that Ifnγ induces expression of miR-92b in YAMC cells. With in silico analysis, we found that the Sirt6 3'-untranslated region (UTR) contains a putative binding site for miR-92b. Luciferase assay showed that Ifnγ inhibited Sirt6 3'-UTR activity and this effect was mimicked by miR-92b via directly targeting the miR-92b seed site in the 3'-UTR of Sirt6 mRNA. Furthermore, Western blot demonstrated that miR-92b downregulated Sirt6 protein expression in YAMC cells. Blocking miR-92b with a specific inhibitor attenuated the inhibitory effect of Ifnγ on Sirt6 protein expression in the cells. Collectively, our data suggest that Ifnγ inhibits Sirt6 protein expression in intestinal epithelial cells via a miR-92b-mediated mechanism. miR-92b may be a novel therapeutic target for rescuing Sirt6 protein levels in intestinal epithelial cells, thereby protecting against intestinal mucosal injury caused by inflammation.

Effects of Derinat on ischemia-reperfusion-induced pressure ulcer mouse model

Sodium salt of deoxyribonucleic acid (DNA), Derinat, isolated from the soft roes of Russian sturgeon, has been utilized as an immunomodulator for the treatment of reactive oxygen species (ROS)-associated diseases in clinics. Here we show that treatment with Derinat has an anti-inflammatory and anti-oxidative effects on cutaneous ischemia-reperfusion (IR) injury in pressure ulcer (PU) model mice. Dorsal skin damage and dermal edema in mild PU model mice were attenuated by treatment with Derinat. Immunohistochemical and biochemical analyses showed that Derinat suppressed IR-induced oxidative damage, i.e. accumulation of 8-hydroxy-2'-deoxyguanosine (8-OHdG), and related inflammatory factors such as cyclooxygenase 2 (COX-2) and IL-6 receptor (IL-6R) in dorsal skin from PU model mice. We also verified that phospholyated/non-phosphorylated ratio of extracellular signal-regulated kinase (Erk) and p38 mitogen-activated protein kinase (MAPK) increased after IR, which were attenuated by Derinat. We then compared the effect of Derinat with that of salmon DNA and other PU therapeutic agents, prostaglandin E1 (PGE1) and basic fibroblast growth factor (bFGF), by using severe PU model mice. The effects of Derinat and salmon-DNA were compatible with those of PGE1 and bFGF. These results suggest that Derinat other fish-derived DNA formulation could be effective enough and become intriguing new therapeutic options.

Sirtuin-6 preserves R-spondin-1 expression and increases resistance of intestinal epithelium to injury in mice

Sirtuin-6 (Sirt6) is a critical epigenetic regulator, but its function in the gut is unknown. Here, we studied the role of intestinal epithelial Sirt6 in colitis-associated intestinal epithelial injury. We found that Sirt6, which is predominantly expressed in epithelial cells in intestinal crypts, is decreased in colitis in both mice and humans. Colitis-derived inflammatory mediators including interferon-γ and reactive oxygen species strongly inhibited Sirt6 protein expression in young adult mouse colonocyte (YAMC) cells. The susceptibility of the cells to injurious insults was increased after knockdown of Sirt6 expression. In contrast, YAMC cells with Sirt6 overexpression exhibited more resistance to injurious insult. Furthermore, intestinal epithelial-specific Sirt6 (Sirt6IEC-KO) knockout mice exhibited greater susceptibility to dextran sulfate sodium (DSS)-induced colitis. RNA sequencing transcriptome analysis revealed that inflammatory mediators such as tumor necrosis factor (TNF)-α suppressed expression of R-spondin-1 (Rspo1, a critical growth factor for intestinal epithelial cells) in Sirt6-silenced YAMC cells in vitro. In addition, lipopolysaccharide was found to inhibit colonic Rspo1 expression in Sirt6IEC-KO mice but not their control littermates. Furthermore, Sirt6IEC-KO mice with DSS-induced colitis also exhibited in a significant decrease in Rspo1 expression in colons. In vitro, knockdown of Rspo1 attenuated the effect of ectopic expression of Sirt6 on protection of YAMC cells against cell death challenges. In conclusion, Sirt6 plays an important role in protecting intestinal epithelial cells against inflammatory injury in a mechanism associated with preserving Rspo1 levels in the cells.

Reduced serum milk fat globule-epidermal growth factor 8 (MFG-E8) concentrations are associated with an increased risk of microvascular complications in patients with type 2 diabetes

BACKGROUND

The association between serum milk fat globule-epidermal growth factor 8 (MFG-E8) concentrations and vascular complications in T2DM remains unclear.

METHODS

A total of 149 patients with T2DM were included. The serum concentrations of MFG-E8, glycosylated hemoglobin (HbA1c), and high-sensitivity C-reactive protein (hs-CRP) were measured.

RESULTS

There was no significant difference in serum MFG-E8 concentrations between the T2DM group and the T2DM with subclinical atherosclerosis (AS) group (615.49±143.54 vs. 596.22±79.46ng/ml, P=0.365), while the serum concentrations of MFG-E8 in the T2DM with microvascular complications group (446.70±61.53ng/ml) and the T2DM with subclinical AS and microvascular complications group (200.87±38.86ng/ml) were significantly lower than those in the T2DM group (P=0.000 for both). In addition, hs-CRP and HbAlc concentrations were independently associated with serum MFG-E8 concentrations (P=0.024 and P=0.01, respectively), and low serum MFG-E8 concentrations were significantly associated with an increased risk of microvascular complications in T2DM patients.

CONCLUSIONS

Serum concentrations of MFG-E8 were negatively associated with the risk of microvascular complications in patients with T2DM. Thus, it might be a potential candidate biomarker for diabetic microvascular complications.

Functional significance of exosomes applied in sepsis: A novel approach to therapy

The nanoparticles referred as exosomes play an active role in intercellular communication. Their potential positive therapeutic effect in bacterial inflammation and sepsis has been the subject of several studies that have examined the feasibility of exosomes as drug-delivery vehicles. The underlying mechanism of interest involves the selective transport of cellular cargo. Most attention has been focused on the exosome-mediated transport of microRNA and protein. Thus, exosomes are expected to be an important tool in the treatment of inflammatory disease. This review covers the relevant literature, focusing on the relationship between exosomes and sepsis and therapeutic use of exosomes in bacterially mediated inflammation or sepsis. We evaluate exosomes as drug vehicles, including their therapeutic cargo, potential mechanisms of action, choice of donor cells, and routes of administration.

Spherical nucleic acid targeting microRNA-99b enhances intestinal MFG-E8 gene expression and restores enterocyte migration in lipopolysaccharide-induced septic mice

Milk fat globule-EGF factor 8 (MFG-E8) maintains the intestinal homeostasis by enhancing enterocyte migration and attenuating inflammation. We previously reported that sepsis is associated with down-regulation of intestinal MFG-E8 and impairment of enterocyte migration. Here, we showed that impairment of intestinal epithelial cell migration occurred in lipopolysaccharide (LPS)-induced septic mice. Treatment of RAW264.7 cells (a murine macrophage-like cell line) with LPS increased expression of miR-99b, a microRNA that is predicted to target mouse MFG-E8 3′UTR. Using a luciferase assay, we showed that miR-99b mimic suppressed the activity of a reporter containing MFG-E8 3′UTR. This suggests the role of miR-99b in inhibition of MFG-E8 gene expression. In addition, we developed an anti-miR99b spherical nucleic acid nanoparticle conjugate (SNA-NC^anti-miR99b). Treatment of both naïve and LPS-challenged cells with SNA-NC^anti-miR99b enhanced MFG-E8 expression in the cells. Administration of SNA-NC^anti-miR99b rescued intestinal MFG-E8 expression in LPS-induced septic mice and attenuated LPS inhibitory effects on intestinal epithelial cell migration along the crypt-villus axis. Collectively, our study suggests that LPS represses MFG-E8 expression and disrupts enterocyte migration via a miR-99b dependent mechanism. Furthermore, this work shows that SNA-NC^anti-miR99b is a novel nanoparticle-conjugate capable of rescuing MFG-E8 gene expression and maintaining intestinal epithelial homeostasis in sepsis.

Milk Fat Globule-Epidermal Growth Factor 8 (MFG-E8) Is a Novel Anti-inflammatory Factor in Rheumatoid Arthritis in Mice and Humans

Milk fat globule-epidermal growth factor 8 (MFG-E8) is an anti-inflammatory glycoprotein that mediates the clearance of apoptotic cells and is implicated in the pathogenesis of autoimmune and inflammatory diseases. Because MFG-E8 also controls bone metabolism, we investigated its role in rheumatoid arthritis (RA), focusing on inflammation and joint destruction. The regulation of MFG-E8 by inflammation was assessed in vitro using osteoblasts, in arthritic mice and in patients with RA. K/BxN serum transfer arthritis (STA) was applied to MFG-E8 knock-out mice to assess its role in the pathogenesis of arthritis. Stimulation of osteoblasts with lipopolysaccharide (LPS) and tumor necrosis factor (TNF)-α downregulated the expression of MFG-E8 by 30% to 35%. MFG-E8-deficient osteoblasts responded to LPS with a stronger production of pro-inflammatory cytokines. In vivo, MFG-E8 mRNA levels were 52% lower in the paws of collagen-induced arthritic (CIA) mice and 24% to 42% lower in the serum of arthritic mice using two different arthritis models (CIA and STA). Similarly, patients with RA (n = 93) had lower serum concentrations of MFG-E8 (-17%) compared with healthy controls (n = 140). In a subgroup of patients who had a moderate to high disease activity (n = 21), serum concentrations of MFG-E8 rose after complete or partial remission had been achieved (+67%). Finally, MFG-E8-deficient mice subjected to STA exhibited a stronger disease burden, an increased number of neutrophils in the joints, and a more extensive local and systemic bone loss. This was accompanied by an increased activation of osteoclasts and a suppression of osteoblast function in MFG-E8-deficient mice. Thus, MFG-E8 is a protective factor in the pathogenesis of RA and subsequent bone loss. Whether MFG-E8 qualifies as a novel biomarker or therapeutic target for the treatment of RA is worth addressing in further studies.